The extracellular matrix (ECM) of an eye is an association of specialized proteins, glycoproteins, and proteoglycans, that subserve and impart structure to the physiological functions of connective tissues. At the cellular level, the ECM not only provides structure, flexibility and support, but also acts as a filtration barrier, mediates cell attachment and influences tissue morphogenesis and differentiation. Part of the normal functioning of the ECM involves the ECM's tightly regulated turnover, which balances the degradation and disposal of effete molecules with the secretion and integration of the various newly synthesized ECM elements.
Specialized extracellular proteolytic enzymes, termed matrix metalloproteinases (MMPs), are produced by many cell types. MMPs play an important role in the initial degradation of such ECM molecules as collagen, fibronectin and various proteoglycans. MMP activity is regulated in part through secretion as inactive proenzymes and activation by proteolytic processing to smaller molecular weight forms. This regulated activity of MMPs usually requires protease activity as well as autolytic mechanisms. MMPs are inhibited by endogenous tissue inhibitors of matrix metalloproteinases (TIMPs). For the MMP, Gelatinase A (GelA) (MMP-2; 72 kD gelatinase; type IV collagenase; E.C. 3.4.24.24), the specific proteolytic activator is known to be another member of the MMP family, namely MT-MMP. In contrast to other MMPs, MT-MMP is predominantly expressed as an integral membrane protein. There are six known subtypes of MT-MMP, hence the designations MT1-MMP for MMP-14, MT2-MMP for MMP-15, MT3-MMP for MMP-16, MT4-MMP for MMP-17, MT5-MMP for MMP-24 and MT6-MMP for MMP-25. All subtypes of MT-MMP, except for MT4-MMP, effect a cleavage in 72 kD proGelA to initiate a proteolytic “cascade” to 66 kD (intermediate), 59 kD (active) and 43 kD (“mini”) forms of GelA. MT-MMP is capable of activating GelA that is complexed with a specific inhibitory protein, TIMP-2. This places MT-MMP expression and/or activity as a major control point in the regulation of ECM turnover.
Trabecular meshwork (TM) is the tissue located at the irido-corneal angle of an eye's anterior segment. The TM is where the aqueous secreted by the ciliary epithelium flows out of the eye. The cells of the TM reside either on collagenous beams, or trabeculae, or embedded in the ECM associated with the canal of Schlemm. The canal of Schlemm is an endothelium-lined channel into which the aqueous drains. The intraocular fluid pressure (IOP) is maintained through a balance of the secretion and outflow of aqueous. Normal IOP is slightly above venous pressure, in part resulting from outflow resistance at the TM. TM outflow resistance is believed to be the result of the hydrodynamic properties of the ECM macromolecules of the TM and the ECM associated with the trabeculae.
For the complex of potentially blinding eye diseases termed primary open angle glaucoma (POAG) the hallmark of which is an insidious, progressive increase in IOP, a prevailing theory of the etiology of the disease is a dysfunction in the regulation of ECM turnover at the level of the TM. There is a biochemical lesion localized to the TM, which manifests as a general excess of ECM or as an imbalance with respect to specific components of the ECM, either of which impairs the ability of fluid to leave the eye at its normal physiological rate. It has been proposed that pharmacological intervention to reduce accumulated ECM could result in a lowering of the elevated IOP characteristic of these diseases.
A therapeutic small organic molecule capable of increasing MT-MMP expression has been decribed by Ito et al. (Ito et al., Eur. J. Biochem. 251, 353-358 (1998)). As described by Ito et al., a trifluoperazine treatment of human cervical fibroblasts resulted in MT1-MMP-induced activation of Gelatinase A (GelA). Trifluoperazine had previously been categorized as a therapeutic “antipsychotic.” Ito et al. however, classified trifluoperazine as a calmodulin antagonist, and made a similar claim for another calmodulin inhibitor, W-7, although the effect from the later compound was not particularly pronounced. Ito et al. deduced that calmodulin negatively regulates MT-MMP expression.
Using Western blot immunochemistry, the presence of MT-MMP has been documented in human ocular tissues other than TM cells, as well as in fresh and cultured porcine TM cells. (Alexander, J. and Acott, T. S., Invest. Ophthalmol. Vis. Sci. 40 (ARVO Abstracts): S506, #2670 (1999)). (Smine, A. and Plantner, J. J., Curr. Eye Res. 16:925 (1997)). In neither case was activation of GelA documented, although Alexander and Acott described increased expression of MT1-MMP with phorbol ester (phorbol 12-myristate 13-acetate). Phorbol ester, however, does not have therapeutic usefulness since it is a known carcinogen.
In addition to trifluoperazine and phorbol ester, the following agents have been shown to increase MT-MMP expression and/or GelA activation in cells other than those of the TM.                Concanavalin A        Interleukin-1α        Orthovanadate        A Hexapeptide derived from Elastin        Cytochalasin D        Monensin        Tumor Necrosis Factor-alpha.        Bacterial Lipopolysaccharide        Hydrogen Peroxide        Oxidized Low Density Lipoproteins        Hepatocyte Growth Factor/Scatter Factor        beta-Amyloid Peptide        Activated Protein C        Growth Hormone        Interleukin VIII        Glycyl-L-Histidyl-L-Lysine-Cu2+        Lysophosphatidic Acid        
A search of U.S. patents found only one patent, U.S. Pat. No. 5,260,059, covering agents that increase the activity of matrix metalloproteinases (MMPs). The '059 patent discloses a method of treating glaucoma by providing TM cells with an array of macromolecules, including matrix metalloproteinase-1 (MMP-1), matrix metalloproteinase-2 (MMP-2) and matrix metalloproteinase-3 (MMP-3). The class of MMPs designated as MT-MMPs had not been characterized at the time the '059 patent was filed. At the time of filing the '059 patent, physiologic activation of GelA was suspected of being brought about by means of autocatalytic mechanisms alone. Other molecules specifically mentioned in the '059 patent are basic heparin-binding growth factor, nerve growth factor, interleukin-1, interleukin-6, phorbol ester, calcium ions, zinc ions, plasmin, trypsin, and aminophenyl mercuric acetate (APMA).
Accordingly, a need still exists in the art to provide compositions and methods for the treatment of diseases termed primary open angle glaucoma.